The present invention relates to a substrate manufacturing apparatus including circuit patterns such as semiconductor devices and liquid crystal and particularly to the technique for inspecting the patterns of substrate in the course of the manufacture using SEM.
A pattern inspecting apparatus using the electron beam of the related art is described, for example, in the official gazette of Japanese Laid-Open Patent Application No. 258703/1993. An example of the pattern inspection apparatus using electron beam described in the above cited reference is illustrated in FIG. 1. An electron beam 2 emitted from an electron beam source 1 is deflected with a deflector 3 in the X direction, this electron beam irradiates an object substrate 5 via an objective lens 4, the secondary electron 7 (including the secondary electron and reflected electron generated from a sample through irradiation of the primary electron beam) emitted from the object substrate 5 is simultaneously deflected with an E×B deflector (hereinafter referred to as only E×B) 13 while a stage 6 is continuously moved in the Y direction, this secondary electron beam 7 is detected with a detector 8 as an electric signal and it is then amplified with a pre-amplifier 14, thereafter the detected signal is A/D-converted with an A/D converter 9 to obtain a digital image, this image is then compared with a digital image at the area which may be expected as to be identical in an image processing circuit 10, thereby an area generating a difference is detected as a pattern defect 11 to identify the defective area. The object substrate 5 is kept at a negative potential with the retarding voltage and therefore an acceleration voltage can easily be changed on the object substrate 5 by changing the retarding voltage 12.
In the apparatus of the related art as illustrated in FIG. 1, the secondary electron 7 has been detected with convergence to one detector 8. However, a degree of convergence of the secondary electron is restricted with various conditions. As the restricting conditions, it is possible to consider (1) degree of freedom of the electro-optical system (retarding voltage, current of primary beam, electric field of the area near the sample, etc. for controlling the acceleration voltage of the primary electron incident to the sample), (2) deflection of the electron beam 2 with the deflector 3 for scanning the sample, (3) allowance of setting, (4) contamination of surface of the detector 7 generated with collision of electron beam and (5) various aberrations in the electro-optical system, or the like.
Although depending on the practical design of the electro-optical system, the conditions (4) and (5) contribute to the degree of convergence of secondary electron and the minimum degree may be estimated as about 1 mm under the condition of the electro-optical system, that is, under the condition that the retarding voltage, current of primary beam and field at the area near the sample which control the acceleration voltage of the primary electron incident to the sample is fixed to only one condition. Moreover, the influence on the degree (2) of convergence of the secondary electron due to the scanning of the deflector 3 with the electron beam 2 appears as the movement of the converging position of about 0.5 mm, although depending on the scanning width and magnifying factor for the secondary electron. Moreover, in regard to the degree of freedom (1) of the optical system, a degree of convergence is changed for about 1 mm by the defocusing, although depending on the other conditions, when the retarding voltage 12, for example, is changed.
Moreover, in actual, since the optical axis of the secondary electron optical system is deviated, it can be estimated that the converging position is shifted by about 0.5 mm. When these factors are added, the diameter of about 3 mm is required for the effective light receiving surface of the detector to detect the secondary electron and when the allowance of setting (3) is considered, the diameter of 4 mm will be required for the effective light receiving surface of the photosensor.
Meanwhile, the frequency characteristic of detector is inversely proportional to the area of the detector. For example, in the case of the detector having the diameter of 4 mm, the cut-off frequency is only 75 MHz even when the design condition and operating condition are improved. On the other hand, when the diameter of detector is set to 2 mm, the cut-off frequency becomes about 150 MHz. However, as explained above, since the detector of the related art requires a diameter of 4 mm, response is possible only for 15 Msps (sps: sample per second) of the sampling frequency corresponding to the cut-off frequency of 75 MHz and it has been impossible to respond to the higher frequency.